Driving device, optical apparatus, and image pickup apparatus

ABSTRACT

A driving device which is capable of increasing a driving speed at which an object to be driven is driven, enhancing quietness in driving the object to be driven, and positioning the object to be driven with high accuracy. A hollow cylindrical magnet ( 1 ) extends along an optical axis, and a plurality of magnetized parts ( 1   a  to  1   j ) spirally extend along the outer peripheral surface of the magnet. A first yoke ( 2 ), a second yoke ( 3 ), a third yoke ( 7 ), and a fourth yoke ( 8 ) are formed of a soft magnetic material, and each of the yokes has five magnetic pole teeth ( 2   a  to  2   e   , 3   a  to  3   e   , 7   a  to  7   e , or  8   a  to  8   e ) each disposed in opposed relation to a corresponding one of the magnetized parts of the magnet. A lens holder ( 12 ) holds the object to be driven and supports the magnet such that the magnet is movable along the optical axis. First and second coils ( 5, 10 ) for magnetizing the first and second yokes, respectively, are energized to move the magnet along the lens holder in the direction along the predetermined axis to thereby drive the object to be driven.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a driving device forelectromagnetically driving an object to be driven, and an opticalapparatus and an image pickup apparatus which are equipped with thedriving device.

2. Description of the Related Art

A lens driving device for cameras has conventionally been proposed e.g.in Japanese Laid-Open Patent Publication (Kokai) No. H11-190815, inwhich a small cylindrical stepping motor is disposed parallel with alens, and the stepping motor drives the lens by means of a lead screw orthe like.

Further, a lens driving device using a voice coil actuator has beendisclosed e.g. in Japanese Laid-Open Patent Publication No. H04-093807.The voice coil actuator is provided with one of a magnet and a coilfixed to a support frame that supports a lens group, and the other to alens barrel, to thereby drive a zoom lens. In this voice coil actuator,the coil is one-phase controlled, and electric current is applied to thecoil in the normal direction or in the reverse direction while detectingthe position of the lens by a position sensor. In this way, the lens ispositioned in a desired position.

In the former driving device, however, noise is generated by slidingcontact between a member held in mesh with the lead screw to function asa female thread and the surface of the lead screw, and hence when thedriving device is used e.g. in a video camera, the sliding noise can berecorded as untoward noise. Further, if the lead screw is deformed, thedeformation can be transmitted to the member serving as the femalethread to cause the member to displace the lens in a directionorthogonal to the optical axis resulting in degraded accuracy in lenspositioning.

Furthermore, when the former driving device is used for driving the zoomlens of a video camera, the driving speed at which the zoom lens isdriven is slow, and hence it takes time to drive the zoom lens to aposition where a desired focal length is obtained, which results indegraded quick shooting performance.

The latter driving device, i.e. the driving device using a voice coilactuator, is superior to the former driving device in zoom speed,quietness, and accuracy in lens positioning. However, in this drivingdevice, the friction coefficients of drive guide parts vary due tochanges in the operating environment and aging. Further, when shootingis performed in an unexpected shooting posture, the lens cannot bepositioned accurately.

Moreover, when the camera is used in an unexpected shooting posture, thelens cannot be accurately controlled to a desired position, and in worstcases suffers from vibration, which hinders the lens from being stoppedat a correct position.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a driving devicewhich is capable of increasing a driving speed at which an object to bedriven, such as a lens, is driven, enhancing quietness in driving theobject to be driven, and positioning the object to be driven with highaccuracy, and an optical apparatus and an image pickup apparatus whichare equipped with the driving device.

To attain the above object, in a first aspect of the present invention,there is provided a driving device for driving an object to be driven,comprising a columnar magnet extending in a direction along apredetermined axis, the magnet having a plurality of magnetized partsspirally extending along an outer peripheral surface thereof, first,second, third, and fourth yokes formed of a soft magnetic material, eachof the yokes having at least one magnetic pole tooth disposed in opposedrelation to a corresponding one of the magnetized parts of the magnet, afirst coil for magnetizing the first yoke and the second yoke, a secondcoil for magnetizing the third yoke and the fourth yoke, and a holdingmember that holds the object to be driven and supports the magnet suchthat the magnet is movable in the direction along the predeterminedaxis, wherein the first and second coils are energized to move themagnet along the holding member in the direction along the predeterminedaxis to thereby drive the object to be driven.

With the construction of the first aspect of the present invention, itis possible to increase a driving speed at which an object to be driven,such as a lens, is driven, enhance quietness in driving the object to bedriven, and position the object to be driven with high accuracy.

Preferably, the driving device comprises a preventive member thatprevents the magnet from rotating about the predetermined axis.

Preferably, the magnet has a shape of a hollow cylinder having a hollowpart formed therethrough, and the holding member is inserted through thehollow part of the magnet.

Preferably, the magnet is fixed to the object to be driven.

To attain the above object, in a second aspect of the present invention,there is provided a driving device for driving an object to be driven,comprising a columnar magnet extending in a direction along apredetermined axis, the magnet having a plurality of magnetized partsspirally extending along an outer peripheral surface thereof, and oneend, first, second, third, and fourth yokes formed of a soft magneticmaterial, each of the yokes having at least one magnetic pole toothdisposed in opposed relation to a corresponding one of the magnetizedparts of the magnet, a first coil for magnetizing the first yoke and thesecond yoke, a second coil for magnetizing the third yoke and the fourthyoke, a base plate to which the one end of the magnet is fixed, acombining member that integrally combines the first, second, third, andfourth yokes, and the first and second coils, and a holding member thatholds the object to be driven and supports the combining member suchthat the combining member is movable in the direction along thepredetermined axis, wherein the first and second coils are energized tomove the magnet along the holding member in the direction along thepredetermined axis to thereby drive the object to be driven.

With the construction of the second aspect of the present invention, itis possible to increase a driving speed at which an object to be driven,such as a lens, is driven, enhance quietness in driving the object to bedriven, and position the object to be driven with high accuracy.

Preferably, the driving device comprises a preventive member thatprevents the combining member from rotating about the predeterminedaxis.

Preferably, the combining member is fixed to the object to be driven.

To attain the above object, in a third aspect of the present invention,there is provided an optical apparatus comprising a driving device asone of those described above.

To attain the above object, in a fourth aspect of the present invention,there is provided a driving device for driving an object to be driven,comprising a magnet to which the object to be driven is fixed, themagnet having at least one magnetized part spirally extending along anouter peripheral surface thereof, a first stator unit comprising a firstyoke formed of a soft magnetic material and having at least one magneticpole tooth, and a first coil for magnetizing the first yoke, and asecond stator unit comprising a second yoke formed of a soft magneticmaterial and having at least one magnetic pole tooth, and a second coilfor magnetizing the second yoke, wherein the magnet is disposed betweenthe first stator unit and the second stator unit, and the magnetic poletooth of each of the first and second yokes spirally extends in opposedrelation to the magnetized part.

Preferably, the driving device further comprises a first bobbin aroundwhich the first coil is wound, and a second bobbin around which thesecond coil is wound, and the first yoke is formed of a pair of yokesfixed to the first bobbin, and the second yoke is formed of a pair ofyokes fixed to the second bobbin.

Preferably, the object to be driven is a lens, and the driving devicefurther comprises a lens holding member holding the lens, a fixingmember that fixes the first and second stator units, a guide memberfixed to the fixing member, for guiding the lens holding member in amanner slidable along an optical axis of the lens, and a rotationpreventive member fixed to the fixing member and engaged with the lensholding member, for preventing rotation of the lens holding member.

With the construction of the fourth aspect of the present invention, themagnet is disposed between the first and second stator units, and themagnetic pole teeth of the first and second yokes are each in the formof a spiral and opposed to respective corresponding ones of themagnetized parts of the magnet. Further, a lens holding member holdingthe lens as the object to be driven is made slidable in a direction inwhich the optical axis extends, but its rotation is inhibited. Thus,reduction of driving time required for driving the lens, enhancement ofquietness in driving the lens, and stable and accurate lens positioning(stability of a stop position) can be achieved.

To attain the above object, in a fifth aspect of the present invention,there is provided an image pickup apparatus comprising a driving deviceas one of those described hereinabove.

The above and other objects, features, and advantages of the presentinvention will become more apparent from the following detaileddescription taken in conjunction with the following drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an exploded perspective view of a driving device according toa first embodiment of the present invention;

FIG. 2 is a side view of the driving device;

FIG. 3 is a longitudinal cross-sectional view of essential parts of thedriving device;

FIG. 4 is a cross-sectional view taken on line C-C in FIG. 3;

FIG. 5 is a developed plan view showing the relationship between yokesand a magnet;

FIG. 6 is an exploded perspective view of a driving device according toa second embodiment of the present invention;

FIG. 7 is a transverse cross-sectional view of essential parts of thedriving device;

FIG. 8 is an exploded perspective view of a driving device according toa third embodiment of the present invention;

FIG. 9 is an exploded perspective view showing the construction of alens driving device implementing a driving device according to a fourthembodiment of the present invention;

FIG. 10 is a side view showing the lens driving device of FIG. 9 in anassembled state;

FIG. 11 is an exploded perspective view showing component partsconstituting a first stator unit of the lens driving device;

FIG. 12 is a perspective view showing the first stator unit of FIG. 11in an assembled state;

FIG. 13 is an exploded perspective view showing component partsconstituting a second stator unit of the lens driving device;

FIG. 14 is a perspective view showing the second stator unit of FIG. 13in an assembled state;

FIG. 15 is a developed plan view showing the relationship between firstand second yokes of the respective first and second stator units and amagnet;

FIG. 16 is a cross-sectional view showing the construction of acomparative example of the lens driving device; and

FIG. 17 is a cross-sectional view showing the construction of anothercomparative example of the lens driving device.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention will now be described in detail below withreference to the drawings showing preferred embodiments thereof.

First, a description will be given of a first embodiment of the presentinvention.

FIG. 1 is an exploded perspective view of a driving device according tothe first embodiment of the present invention. FIG. 2 is a side view ofthe driving device, FIG. 3 a longitudinal cross-sectional view ofessential parts of the driving device, FIG. 4 a cross-sectional viewtaken on line C-C in FIG. 3, and FIG. 5 a developed plan view showingthe relationship between yokes and a magnet. In the followingdescription, it is assumed that the driving device of the presentembodiment is used as a driving device for driving a lens of a camera.

As shown in FIG. 1, the driving device is comprised of a hollowcylindrical magnet 1, a first yoke 2, a second yoke 3, a third yoke 7,and a fourth yoke 8. The magnet 1 has an outer peripheral surfacethereof formed with a plurality of magnetized parts 1 a, 1 b, 1 c, 1 d,1 e, 1 f, 1 g, 1 h, 1 i, and 1 j. The magnetized parts 1 a to 1 jspirally extend along the outer peripheral surface of the magnet 1 andadjacent to one another. Among the magnetized parts 1 a to 1 j, themagnetized parts 1 a, 1 c, 1 e, 1 g, and 1 i are S magnetized, while themagnetized parts 1 b, 1 d, 1 f, 1 h, and 1 j are N magnetized. In thepresent embodiment, the magnet 1 has ten magnetized parts, and in atransverse cross section of the magnet 1, the ten magnetized parts arecircumferentially arranged alternately as N and S poles as shown in FIG.4. It is to be understood that the number of magnetized parts (poles) isnot limited to the above number.

The magnet 1 has a hollow part 1 k (guide part) axially formedtherethrough, and a guide bar 14, referred to hereinafter, is slidablyfitted in the hollow part 1 k. This enables the magnet 1 to move alongits axis while being guided by the guide bar 14.

The first yoke 2 is formed of a soft magnetic material, and has fivespiral magnetic pole teeth 2 a, 2 b, 2 c, 2 d, and 2 e. If the number ofthe magnetized poles of the magnet 1 is equal to N, the magnetic poleteeth are arranged at phase intervals of 4π/N (rad) in terms ofmechanical angle, i.e. at phase intervals of 2π (rad) in terms ofelectrical angle, and the number of the magnetic pole teeth is equal toN/2. In the present embodiment, since N is equal to 10, the magneticpole teeth are arranged at phase intervals of 2π/5 (rad), and the numberof the magnetic pole teeth is equal to 5. The magnetic pole teeth 2 a, 2b, 2 c, 2 d, and 2 e are opposed to respective corresponding ones of themagnetized parts of the magnetic 1.

The second yoke 3 is formed of a soft magnetic material, and has fivespiral magnetic pole teeth 3 a, 3 b, 3 c, 3 d, and 3 e. The number ofthe magnetic pole teeth of the second yoke 3 is determined similarly tothat of the magnetic pole teeth of the first yoke 2, and the magneticpole teeth 3 a, 3 b, 3 c, 3 d, and 3 e are opposed to respectivecorresponding ones of the magnetized parts of the magnet 1. Further, asshown in FIG. 5, the magnetic pole teeth 3 a, 3 b, 3 c, 3 d, and 3 e arearranged in a manner shifted in phase from the magnetic pole teeth 2 a,2 b, 2 c, 2 d, and 2 e, respectively, by 2π/N (rad) in terms ofmechanical angle (π (rad) in terms of electrical angle).

A first bobbin 4 is disposed between the first yoke 2 and the secondyoke 3. The first bobbin 4 is formed of a non-conductive material, suchas plastic, and a first coil 5 made of a lead wire is wound around thefirst bobbin 4. When an electric current is applied to the first coil 5,the magnetic pole teeth 2 a to 2 e of the first yoke 2 and the magneticpole teeth 3 a to 3 e of the second yoke 3 are magnetized to haverespective predetermined polarities.

The first yoke 2 and the second yoke 3 are fixed to a first outer cover6. The first outer cover 6 is formed of a soft magnetic material. Thefirst outer cover 6 not only covers the first bobbin 4 and the firstcoil 5, but also magnetically couples the first yoke 2 and the secondyoke 3 to each other for relative positioning of the two yokes 2 and 3.

The first yoke 2, the second yoke 3, the first bobbin 4, the first coil5, and the first outer cover 6 form a first stator.

The third yoke 7 is formed of a soft magnetic material, and has fivespiral magnetic pole teeth 7 a, 7 b, 7 c, 7 d, and 7 e. The number ofthe magnetic pole teeth of the third yoke 7 is determined similarly tothat of the magnetic pole teeth of the first yoke 2, and the magneticpole teeth 7 a, 7 b, 7 c, 7 d, and 7 e are opposed to respectivecorresponding ones of the magnetized parts of the magnet 1.

The fourth yoke 8 is formed of a soft magnetic material, and has fivespiral magnetic pole teeth 8 a, 8 b, 8 c, 8 d, and 8 e. The number ofthe magnetic pole teeth of the fourth yoke 8 is determined similarly tothat of the magnetic pole teeth of the first yoke 2, and the magneticpole teeth 8 a, 8 b, 8 c, 8 d, and 8 e are opposed to respectivecorresponding ones of the magnetized parts of the magnet 1. Further, asshown in FIG. 5, the magnetic pole teeth 8 a, 8 b, 8 c, 8 d, and 8 e arearranged in a manner shifted in phase from the magnetic pole teeth 7 a,7 b, 7 c, 7 d, and 7 e, respectively, by 2π/N (rad) in terms ofmechanical angle (π (rad) in terms of electrical angle).

A second bobbin 9 is disposed between the third yoke 7 and the fourthyoke 8. The second bobbin 9 is formed of a non-conductive material, suchas plastic, and a second coil 10 made of a lead wire is wound around thesecond bobbin 9. When an electric current is applied to the second coil10, the magnetic pole teeth 7 a to 7 e of the third yoke 7 and themagnetic pole teeth 8 a to 8 e of the fourth yoke 8 are magnetized tohave respective predetermined polarities.

The third yoke 7 and the fourth yoke 8 are fixed to a second outer cover11. The second outer cover 11 is formed of a soft magnetic material. Thesecond outer cover 11 not only covers the second bobbin 9 and the secondcoil 10, but also magnetically couples the third yoke 7 and the fourthyoke 8 to each other for relative positioning of the two yokes 7 and 8.

The third yoke 7, the fourth yoke 8, the second bobbin 9, the secondcoil 10, and the second outer cover 11 form a second stator.

When the relationship between the first yoke 2, the second yoke 3, thethird yoke 7, and the fourth yoke 8, and the magnetized parts 1 a to 1 jof the magnet 1 is illustrated in a developed manner, as shown in FIG.5, the first stator and the second stator are arranged in a mannershifted in phase from each other with respect to the magnetization phaseof the magnetized parts of the magnet 1 by π/N (rad) in terms ofmechanical angle (by π/2 (rad) in terms of electrical angle i.e.), thatis, in the present embodiment, by π/10 (rad) in terms of mechanicalangle, because each of the first stator and the second stator has tenmagnetic pole teeth (the magnetic pole teeth 2 a to 2 e and 3 a to 3 eof the first stator or the magnetic pole teeth 7 a to 7 e and 8 a to 8 eof the second stator). The first stator and the second stator are fixedto each other by a known method, such as welding or bonding.

The magnet 1 has a lens holder 12 attached thereto. The lens holder 12is formed with an arm 12 a and a groove 12 b. The lens holder 12 isformed integrally with the magnet 1 with the arm 12 a joined to themagnet 1. The lens holder 12 has a lens 13 fixed thereto.

The guide bar 14 is slidably fitted in the hollow part 1 k of the magnet1, as shown in FIG. 3, and the magnet 1 is movably supported by theguide bar 14. The guide bar 14 guides the magnet 1 for axial movementthereof. A shake preventive guide bar 15 is slidably fitted in thegroove 12 b of the lens holder 12, for preventing the magnet 1 fromrotating about its axis. More specifically, the shake preventive guidebar 15 prevents the lens holder 12 and the lens 13 from rotating aboutthe axis of the magnet 1 (i.e. about the guide bar 14).

As shown in FIG. 2, the first stator and the second stator are fixed toa base plate 16. The base plate 16 is formed therein with an opening 16a coaxial with the lens 13, a hole 16 c, and a hole 16 b and providedwith an arm 16 d. The opening 16 a guides light having passed throughthe lens 13 toward a camera body, not shown. The arm 16 d is formedtherein with a hole 16 e axially aligned with the hole 16 c. The guidebar 14 is inserted through the hole 16 c with one end thereof fitted inthe hole 16 e and fixed thereto. The shake preventive guide bar 15 issecured to the base plate 16 at one end thereof fitted in the hole 16 b.

Next, a description will be given of the operation of the drivingdevice.

It is assumed that in a state shown in FIG. 5, the first coil 5 isenergized such that the magnetic pole teeth 2 a, 2 b, 2 c, 2 d, and 2 eof the first yoke 2 are S magnetized, and the magnetic pole teeth 3 a, 3b, 3 c, 3 d, and 3 e of the second yoke 3 are N magnetized. Whenenergization of the first coil 5 is interrupted and at the same time thesecond coil 10 is energized such that the magnetic pole teeth 7 a, 7 b,7 c, 7 d, and 7 e of the third yoke 7 are N magnetized, and the magneticpole teeth 8 a, 8 b, 8 c, 8 d, and 8 e of the fourth yoke 8 are Smagnetized, an electromagnetic force acting in a direction indicated byan arrow A in FIG. 5 is generated in the magnet 1. The electromagneticforce acting in the direction indicated by the arrow A is divided into acomponent acting in a direction of rotating the magnet 1 and a componentacting along the axis of the magnet 1.

Since the shake preventive guide bar 15 prevents the lens holder 12fixed to the magnet 1 from rotating about the guide bar 14, even whenthe component of the electromagnetic force generated in the directionindicated by the arrow A, which acts in the direction of rotating themagnet 1, is applied to the magnet 1, the magnet 1 (the lens holder 12and the lens 13) is not rotated, but moved along the guide bar 14 in adirection indicated by an arrow B in FIG. 5 (i.e. an upward direction asviewed in FIG. 2) by the component acting along the axis of the magnet 1in the same direction. Then, the magnet 1 is stopped at a position wherethe magnetized part 1 i is opposed to the magnetic pole tooth 7 a of thethird yoke 7.

Then, when energization of the second coil 10 is interrupted in thisstate, and at the same time the first coil 5 is energized such that themagnetic pole teeth 2 a, 2 b, 2 c, 2 d, and 2 e of the first yoke 2 areN magnetized, and the magnetic pole teeth 3 a, 3 b, 3 c, 3 d, and 3 e ofthe second yoke 3 are S magnetized, an electromagnetic force acting inthe direction indicated by the arrow A is generated again in the magnet1. In this case as well, even when the component of the electromagneticforce generated in the direction indicated by the arrow A, which acts inthe direction of rotating the magnet 1, is applied to the magnet 1, themagnet 1 is not rotated, but moved along the guide bar 14 in thedirection indicated by the arrow B (the upward direction as viewed inFIG. 2) by the component acting in the same direction. Then, the magnet1 is stopped at a position where the magnetized part 1 i is opposed tothe magnetic pole tooth 2 a of the first yoke 2.

Then, when energization of the first coil 5 is interrupted in thisstate, and at the same time the second coil 10 is energized such thatthe magnetic pole teeth 7 a, 7 b, 7 c, 7 d, and 7 e of the third yoke 7are S magnetized, and the magnetic pole teeth 8 a, 8 b, 8 c, 8 d, and 8e of the fourth yoke 8 are N magnetized, an electromagnetic force actingin the direction indicated by the arrow A is generated again in themagnet 1. In this case as well, even when the component of theelectromagnetic force generated in the direction indicated by the arrowA, which acts in the direction of rotating the magnet 1, is applied tothe magnet 1, the magnet 1 is not rotated, but moved along the guide bar14 in the direction indicated by the arrow B by the component acting inthe same direction. Then, the magnet 1 is stopped at a position wherethe magnetized part 1 j is opposed to the magnetic pole tooth 7 a of thethird yoke 7.

Then, when energization of the second coil 10 is interrupted in thisstate, and at the same time the first coil 5 is energized such that themagnetic pole teeth 2 a, 2 b, 2 c, 2 d, and 2 e of the first yoke 2 areS magnetized, and the magnetic pole teeth 3 a, 3 b, 3 c, 3 d, and 3 e ofthe second yoke 3 are N magnetized, an electromagnetic force acting inthe direction indicated by the arrow A is generated again in the magnet1. In this case as well, even when the component of the electromagneticforce generated in the direction indicated by the arrow A, which acts inthe direction of rotating the magnet 1, is applied to the magnet 1, themagnet 1 is not rotated, but moved along the guide bar 14 in thedirection indicated by the arrow B by the component acting in the samedirection. Then, the magnet 1 is stopped at a position where themagnetized part 1 j is opposed to the magnetic pole tooth 2 a of thefirst yoke 2.

To move the magnet 1 in the opposite direction to the directionindicated by the arrow B, the coils 5 and 10 are only required to bealternately energized or deenergized in a sequence reverse to the abovedescribed sequence.

Thus, the first coil 5 and the second coil 10 are alternately energizedor deenergized to switch the polarity of each of the magnetic pole teeth2 a to 2 e of the first yoke 2, the magnetic pole teeth 3 a to 3 e ofthe second yoke 3, the magnetic pole teeth 7 a to 7 e of the third yoke7, and the magnetic pole teeth 8 a to 8 e of the fourth yoke 8, wherebythe magnet 1 (the lens holder 12 and the lens 13) can be moved along theguide bar 14 in the direction indicated by the arrow B or in theopposite direction.

Further, it is possible to carry out micro-step control such that themagnet 1 is stopped at a position corresponding to the magnitude ofmagnetic forces generated by the first coil 5 and the second coil 10,such as a position where the magnetized parts are not just opposed torespective corresponding ones of the magnetic pole teeth, by controllingthe magnitude of electric currents applied to the first coil 5 and thesecond coil 10. According to this method, the magnet 1 is stably held ina position where it is attracted by the two-phase coils, so that thelens 13 can be positioned more stably and accurately than by theconventional method using a voice coil actuator including a one-phasecoil.

Further, according to the present embodiment, the first coil 5 and thesecond coil 10 are alternately switched for energization to therebydrive the lens holder 12 and the lens 13 along the optical axis byelectromagnetic forces. Therefore, as is distinct from the conventionaltype driving device which rotates a lead screw by a stepping motor todrive the lens along the optical axis, the driving device according tothe present embodiment is free from generation of sliding noise and aslow lens driving speed. Further, the driving device according to thepresent embodiment is capable of performing quiet and high-speed lensdriving similarly to the conventional type driving device using a voicecoil actuator including a one-phase coil.

Further, in the present embodiment, the hollow cylindrical magnet 1 isused to facilitate assembly of the first yoke 2 and the second yoke 3and that of the third yoke 7 and the fourth yoke 8. Since each of theyokes 2, 3, 7, and 8 has magnetic pole teeth thereof spirally extendingalong the outer periphery of the magnet 1, the first yoke 2 and thesecond yoke 3 can be assembled together by spirally rotating and axiallymoving the two yokes according to the spiral shape of the magnetic poleteeth. This facilitates assembly of the first yoke 2 and the second yoke3. This is also the case with the third yoke 7 and the fourth yoke 8.

Furthermore, the use of the driving device of the present embodimentmakes it possible to provide a camera which is capable of not onlypositioning its lens stably with high accuracy, but also performingquiet and high-speed lens driving.

Although in the present embodiment, the hollow part 1 k of the magnet 1is formed as a guide part for the guide bar 14, this is not limitative,but, for example, the lens holder 12 which is movable in unison with themagnet 1 may be formed therein with a guide hole in which the guide bar14 is slidably fitted.

Next, a second embodiment of the present invention will be describedwith reference to FIGS. 6 and 7.

FIG. 6 is an exploded perspective view of a driving device according tothe second embodiment, and FIG. 7 is a transverse cross-sectional viewof essential parts of the driving device.

The present embodiment is distinguished from the first embodiment inthat a magnet having a shape of a quadrangular prism, i.e. a rectangulartransverse cross-section, is used. In the present embodiment, elementsand parts corresponding to those of the first embodiment are designatedby identical reference numerals, and description thereof is omitted.

As shown in FIG. 6, the driving device of the present embodiment iscomprised of the quadrangular prism-shaped magnet 101, a first yoke 102,a second yoke 103, a third yoke 107, and a fourth yoke 108, each yokehaving a rectangular plate-like shape. The magnet 101 has an outerperipheral surface thereof formed with a plurality of magnetized parts101 a, 101 b, 101 c, 101 d, 101 e, 101 f, 101 g, 101 h, 101 i, and 101j. The magnetized parts 101 a to 101 j spirally extend along the outerperipheral surface of the magnet 101 and adjacent to one another. Amongthe magnetized parts 101 a to 101 j, the magnetized parts 101 a, 101 c,101 e, 101 g, and 101 i are S magnetized, while the magnetized parts 101b, 101 d, 101 f, 101 h, and 101 j are N magnetized. In the presentembodiment, the magnet 101 has ten magnetized parts, but the number ofmagnetized parts (poles) is not limited to ten.

The magnet 101 has a hollow part 101 k (guide part) axially formedtherethrough and having a circular transverse cross-section, and theguide bar 14 is slidably fitted in the hollow part 101 k. Thus, themagnet 101 is supported such that it can move along its axis while beingguided by the guide bar 14.

The first yoke 102 is formed of a soft magnetic material, and has twospiral magnetic pole teeth 102 a and 102 b. The magnetic pole teeth 102a and 102 b are opposed to respective corresponding ones of themagnetized parts of the magnet 101. Further, the magnetic pole teeth 102a and 102 b are the same in phase with each other with respect to thepolarity of respective opposed corresponding ones of the magnetizedparts of the magnet.

The second yoke 103 is formed of a soft magnetic material, and has twospiral magnetic pole teeth 103 a and 103 b. The magnetic pole teeth 103a and 103 b are opposed to respective corresponding ones of themagnetized parts of the magnet 101. Further, the magnetic pole teeth 103a and 103 b are the same in phase with each other with respect to thepolarity of the respective opposed corresponding ones of the magnetizedparts of the magnet. Similarly to the first embodiment, the magneticpole teeth 103 a and 103 b are arranged in a manner shifted in phasefrom the magnetic pole teeth 102 a and 102 b, respectively, by amagnetization pitch thereof (the distance between the center of an Spole and that of an N pole), i.e. by π (rad) in terms of electricalangle with respect to the magnetization phase of the magnetized parts ofthe magnet 1.

A first bobbin 104 is disposed between the first yoke 102 and the secondyoke 103. The first bobbin 104 is formed of a non-conductive material,such as plastic, and a first coil 105 made of a lead wire is woundaround the first bobbin 104. When an electric current is applied to thefirst coil 105, the magnetic pole teeth 102 a and 102 b of the firstyoke 102 and the magnetic pole teeth 103 a and 103 b of the second yoke103 are magnetized to have respective predetermined polarities.

The first yoke 102 and the second yoke 103 are fixed to a first outercover 106. The first outer cover 106 is formed of a soft magneticmaterial. The first outer cover 106 not only covers the first bobbin 104and the first coil 105, but also magnetically couples the first yoke 102and the second yoke 103 to each other for relative positioning of thetwo yokes 102 and 103.

The first yoke 102, the second yoke 103, the first bobbin 104, the firstcoil 105, and the first outer cover 106 form a first stator.

The third yoke 107 is formed of a soft magnetic material, and has twospiral magnetic pole teeth 107 a and 107 b. The magnetic pole teeth 107a and 107 b are opposed to respective corresponding ones of themagnetized parts of the magnet 101. Further, the magnetic pole teeth 107a and 107 b are the same in phase with each other with respect to thepolarity of the respective opposed corresponding ones of the magnetizedparts of the magnet.

The fourth yoke 108 is formed of a soft magnetic material, and has twospiral magnetic pole teeth 108 a and 108 b. The magnetic pole teeth 108a and 108 b are opposed to respective corresponding ones of themagnetized parts of the magnet 101. Further, the magnetic pole teeth 108a and 108 b are the same in phase with each other with respect to thepolarity of respective opposed corresponding ones of the magnetizedparts of the magnet. Similarly to the first embodiment, the magneticpole teeth 108 a and 108 b are arranged in a manner shifted in phasefrom the magnetic pole teeth 107 a and 107 b, respectively, by amagnetization pitch thereof (the distance between the center of an Spole and that of an N pole), i.e. by π (rad) in terms of electricalangle with respect to respective corresponding ones of the magnetizedparts of the magnet 1.

A second bobbin 109 is disposed between the third yoke 107 and thefourth yoke 108. The second bobbin 109 is formed of a non-conductivematerial, such as plastic, and a second coil 110 made of a lead wire iswound around the second bobbin 109. When an electric current is appliedto the second coil 110, the magnetic pole teeth 107 a and 107 b of thethird yoke 107 and the magnetic pole teeth 108 a and 108 b of the fourthyoke 108 are magnetized to have respective predetermined polarities.

The third yoke 107 and the fourth yoke 108 are fixed to a second outercover 111. The second outer cover 111 is formed of a soft magneticmaterial. The second outer cover 111 not only covers the second bobbin109 and the second coil 110, but also magnetically couples the thirdyoke 107 and the fourth yoke 108 to each other for relative positioningof the two yokes 107 and 108.

The third yoke 107, the fourth yoke 108, the second bobbin 109, thesecond coil 110, and the second outer cover 111 form a second stator.Similarly to the first embodiment, the second stator and the firststator are arranged in a manner shifted in phase from each by π/2 (rad)in terms of electrical angle with respect to the magnetization phase ofthe magnetized parts of the magnet 1.

In the present embodiment, similarly to the first embodiment, the firstcoil 105 and the second coil 110 are alternately energized ordeenergized to switch the polarity of each of the magnetic pole teeth ofthe first yoke 102 and the magnetic pole teeth of the second yoke 103,whereby the magnet 101 (the lens holder 12 and the lens 13) can be movedalong the guide bar 14.

According to the present embodiment configured as above, since themagnet 101 in the form of a quadrangular prism is used as shown in FIG.7, a dimension D (the size of the magnet 101 in the diametral directionof the lens 13) can be reduced. Therefore, when the driving device ofthe present embodiment is incorporated e.g. in the lens barrel of acamera, the lens barrel can have a reduced diameter.

Next, a third embodiment of the present invention will be described withreference to FIG. 8. FIG. 8 is an exploded perspective view of a drivingdevice according to the third embodiment.

As shown in FIG. 8, the present embodiment is distinguished from thefirst embodiment in that a magnet 201 is fixed to a base plate 216, anda first stator and a second stator are fixed to a lens holder 212. Thefirst stator is comprised of the first yoke 2, the second yoke 3, thefirst bobbin 4, the first coil 5, and the first outer cover 6. Thesecond stator is comprised of the third yoke 7, the fourth yoke 8, thesecond bobbin 9, the second coil 10, and the second outer cover 11.

The magnet 201 is in the form of a cylinder extending parallel with theoptical axis, and has one end thereof fixed to the base plate 216. Themagnet 201 has an outer peripheral surface thereof formed with aplurality of magnetized parts 201 a, 201 b, 201 c, 201 d, 201 e, 201 f,201 g, 201 h, 201 i, and 201 j. The magnetized parts 201 a to 201 jspirally extend along the outer peripheral surface of the magnet 201 andadjacent to one another. Among the magnetized parts 201 a to 201 j, themagnetized parts 201 a, 201 c, 201 e, 201 g, and 201 i are S magnetized,while the magnetized parts 201 b, 201 d, 201 f, 201 h, and 201 j are Nmagnetized. In the present embodiment, the magnet 201 has ten magnetizedparts, but the number of magnetized parts (poles) is not limited to ten.

A guide bar 214 and a shake preventive guide bar 215 both extendingparallel with the magnet 201 are fixed to the base plate 216. As will bedescribed hereinafter, the guide bar 214 supports the lens holder 212such that it is movable along the optical axis. The shake preventiveguide bar 215 prevents rotation of the lens holder 212 about the opticalaxis, as described hereinafter.

The lens holder 212 is formed with an arm 212 a, a guide part 212 c, anda groove 212 b. The first and second stators are fixed to the arm 212 a.The guide bar 214 fixed to the base plate 216 is slidably fitted in theguide part 212 c, while the shake preventive guide bar 215 is slidablyfitted in the groove 212 b.

In the present embodiment configured as above, as is the case with thefirst embodiment, the first coil 5 and the second coil 10 arealternately energized, and as a consequence, electromagnetic forces aregenerated between the magnet 201 and the yokes 2, 3, 7, and 8 to movethe magnet 201 (the lens holder 212 and the lens 13) along the guide bar214 in the direction of the optical axis.

Therefore, according to the present embodiment, the same advantageouseffects as provided by the first embodiment can be obtained.

Next, a fourth embodiment of the present invention will be describedwith reference to FIGS. 9 to 17.

FIG. 9 is an exploded perspective view showing the construction of alens driving device as a driving device according to the presentembodiment, and FIG. 10 is a side view showing the lens driving devicein an assembled state. FIG. 11 is an exploded perspective view showingcomponent parts constituting a first stator unit, and FIG. 12 aperspective view showing the first stator unit in an assembled state.FIG. 13 is an exploded perspective view showing component partsconstituting a second stator unit, and FIG. 14 a perspective viewshowing the second stator unit in an assembled state. FIG. 15 is adeveloped plan view showing the relationship between respective firstand second yokes of the first and second stator units, and a magnet.

The lens driving device in FIGS. 9 to 15 is comprised of the magnet 301,the first stator unit formed of the first yoke 302, the second yoke 303,a first bobbin 304, and a first coil 305, the second stator unit formedof a third yoke 306, a fourth yoke 307, a second bobbin 308, and asecond coil 309, a lens holder 310, and a base plate 314.

The magnet 301 is in the form of a rectangular parallelepiped, and hasan outer peripheral surface thereof formed with a plurality ofmagnetized parts 301 a, 301 b, 301 c, 301 d, 301 e, 301 f, 301 g, 301 h,301 i, 301 j, 301 k, 3011, 301 m, and 301 n. Although in the followingdescription, it is assumed that the magnet 301 has the magnetized parts301 a to 301 n, the number of magnetized parts is not limited to 14 (ato n). The magnetized parts 301 a to 301 n spirally extend along theouter peripheral surface of the magnet 301 and adjacent to one another(see FIG. 15). The magnetized parts 301 a, 301 c, 301 e, 301 g, 301 i,301 k, and 301 m are S magnetized, while the magnetized parts 301 b, 301d, 301 f, 301 h, 301 j, 301 l, and 301 n are N magnetized, for example.In short, the magnetized parts 301 a to 301 n are magnetized so as toprovide alternately different poles.

The first yoke 302 is formed of a soft magnetic material, and has aspiral magnetic pole tooth 302 a which is opposed to a corresponding oneof the spirally magnetized parts 301 a to 301 n on the outer peripheralsurface of the magnet 301 (see FIG. 15). The first yoke 302 is insertedand fixed in a space part of the first bobbin 304, referred tohereinafter. The magnetic pole tooth 302 a has a flat plate shape andextends in the same direction as a direction in which the magnetizedparts 301 a to 301 n of the magnet 301 are spirally formed.

The second yoke 303 is formed of a soft magnetic material, and has aspiral magnetic pole tooth 303 a which is opposed to a corresponding oneof the spirally magnetized parts 301 a to 301 n on the outer peripheralsurface of the magnet 301 (see FIG. 15). The second yoke 303 is alsoinserted and fixed in the space part of the first bobbin 304, referredto hereinafter. The magnetic pole tooth 303 a has a flat plate shape andextends in the same direction as a direction in which the magnetizedparts 301 a to 301 n of the magnet 301 are spirally formed.

The first bobbin 304 is formed of a non-conductive material (e.g.plastic). The first bobbin 304 is formed therein with the space part inwhich the respective flat plate parts of the first and second yokes 302and 303 can be inserted. Further, the first bobbin 304 has an outerperiphery formed as a winding part around which the first coil 305 iswound. The first yoke 302 and the second yoke 303 are inserted into thespace part of the first bobbin 304 from respective opposite directionsand fixed in the same (see FIGS. 11 and 12).

The first coil 305 is formed by a lead wire wound around the firstbobbin 304. When the first coil 305 is energized, the magnetic poletooth 302 a of the first yoke 302 and the magnetic pole tooth 303 a ofthe second yoke 303 are magnetized to have respective predeterminedpolarities. In the present embodiment, the magnetic pole tooth 302 a ofthe first yoke 302 and the magnetic pole tooth 303 a of the second yoke303 are positioned in a manner shifted in phase from each other by themagnetization pitch P of the magnet 301, as shown in FIG. 15.

The first yoke 302, the second yoke 303, the first bobbin 304, and thefirst coil 305 form the first stator unit, as described hereinbefore.

The third yoke 306 is formed of a soft magnetic material, and has aspiral magnetic pole tooth 306 a which is opposed to a corresponding oneof the spirally magnetized parts 301 a to 301 n on the outer peripheralsurface of the magnet 301 (see FIG. 15). The third yoke 306 is insertedand fixed in a space part of the second bobbin 308, referred tohereinafter. The magnetic pole tooth 306 a has a flat plate shape andextends in the same direction as a direction in which the magnetizedparts 301 a to 301 n of the magnet 301 are spirally formed.

The fourth yoke 307 is formed of a soft magnetic material, and has aspiral magnetic pole tooth 307 a which is opposed to a corresponding oneof the spirally magnetized parts 301 a to 301 n on the outer peripheralsurface of the magnet 301 (see FIG. 15). The fourth yoke 307 is alsoinserted and fixed in the space part of the second bobbin 308, referredto hereinafter. The magnetic pole tooth 307 a has a flat plate shape andextends in the same direction as a direction in which the magnetizedparts 301 a to 301 n of the magnet 301 are spirally formed.

The second bobbin 308 is formed of a non-conductive material (e.g.plastic). The second bobbin 308 is formed therein with the space part inwhich the respective flat plate parts of the third and fourth yokes 306and 307 can be inserted. Further, the second bobbin 308 has an outerperiphery formed as a winding part around which the second coil 309 iswound. The third yoke 306 and the fourth yoke 307 are inserted into thespace part of the second bobbin 308 from respective opposite directionsand fixed in the same (see FIGS. 13 and 14).

The second coil 309 is formed by a lead wire wound around the secondbobbin 308. When the second coil 309 is energized, the magnetic poletooth 306 a of the third yoke 306 and the magnetic pole tooth 307 a ofthe fourth yoke 307 are magnetized to have respective predeterminedpolarities. In the present embodiment, the magnetic pole tooth 306 a ofthe third yoke 306 and the magnetic pole tooth 307 a of the fourth yoke307 are positioned in a manner shifted in phase from each other by themagnetization pitch P of the magnet 301, as shown in FIG. 15.

The third yoke 306, the fourth yoke 307, the second bobbin 308, and thesecond coil 309 form the second stator unit, as described hereinbefore.

As shown in FIG. 10, the first stator unit and the second stator unitare fixed to the base plate 314 in a manner sandwiching the magnet 301,with the magnetic pole teeth 302 a, 303 a, 306 a, and 307 a of the twostator units opposed to the magnet 301. In short, the magnet 301 isdisposed between the first stator unit and the second stator unit.

Further, as shown in FIG. 15, the magnetic pole teeth of the firststator unit and the second stator unit are arranged in a manner shiftedin phase from each other with respect to the magnetization phase of themagnetized parts of the magnet 301 by 90 degrees in terms of electricalangle, and shifted in position from by P×(2n+1)/2 in terms of mechanicalposition, in which P represents the magnetization pitch, and nrepresents an arbitrary integer. In FIG. 15, the magnetized parts 301 ato 301 n of the magnet 301 are indicated by two-dot chain lines.

The lens holder 310 is comprised of a main body formed into a shapehaving an inner diameter part in which a lens 311 can be fitted, an arm310 a, a guide part 310 b, and a groove 310 c. The arm 310 a projectsradially outward from the main body of the lens holder 310. The arm 310a is secured to the magnet 301, whereby the lens holder 310 isintegrally combined with the magnet 301. The guide part 310 b projectsradially outward from the main body of the lens holder 310 and extendsin the axial direction. The guide part 310 b is formed therein with athrough hole 310 d through which a guide bar 312 is slidably fitted.

The lens 311 is rigidly fitted in the inner diameter part of the mainbody of the lens holder 310 and is used for photographing by an imagepickup apparatus (not shown) incorporating the lens driving device ofthe present embodiment.

As shown in FIG. 10, the guide bar 312 is axially movably fitted throughthe through hole 310 d of the guide part 310 b of the lens holder 310,with one axial end thereof rigidly fitted in a hole 314 d formed in anarm 314 c of the base plate 314, referred to hereinafter. The guide bar312 guides the lens holder 310 such that the lens holder 310 can slideparallel with the optical axis.

A shake preventive guide bar 313 is slidably fitted in the groove 310 cof the lens holder 310, with one axial end thereof rigidly fitted in ahole 314 b formed in an main body of the base plate 314. The shakepreventive guide bar 313 prevents rotation of the lens holder 310 aboutthe guide bar 312.

The main body of the base plate 314 is formed into a general annularshape. Further, the base plate 314 is comprised of an opening 314 a, thehole 314 b, the arm 314 c, and the hole 314 d. As shown in FIG. 10, thebase plate 314 has the first stator unit and the second stator unitsecured thereto. The opening 314 a passes light transmitted through thelens 311. The light having passed through the opening 314 a is guided toa predetermined position. The shake preventive guide bar 313 is fixedlyinserted in the hole 314 b formed in the main body of the base plate314. The arm 314 c axially extends from the main body of the base plate314, and has a semi-circular shape in cross section which enables theguide part 310 b of the lens holder 310 to be disposed therein with aslight gap. The guide bar 312 is fixedly inserted in the hole 314 dformed in the arm 314 c.

As stated above, the guide bar 312 is axially slidably fitted throughthe through hole 310 d of the guide part 310 b of the lens holder 310,with the axial end thereof rigidly fitted in the hole 314 d of the baseplate 314. This enables the lens holder 310 to slide relative to thebase plate 314 via the guide bar 312 in the direction parallel with theoptical axis. Further, the shake preventive guide bar 313 is slidablyfitted in the groove 310 c of the lens holder 310, with the axial endthereof rigidly fitted in the hole 314 b of the base plate 314. Thisenables the lens holder 310 and the lens 311 to move only along theoptical axis without rotating about the guide bar 312.

Next, the operation of the lens driving device of the present embodimentconstructed as above will be described with reference to FIGS. 9 to 17.

As stated above, among the magnetized parts 301 a to 301 n of the magnet301, the magnetized parts 301 a, 301 c, 301 e, 301 g, 301 i, 301 k, and301 m are S magnetized, while the magnetized parts 301 b, 301 d, 301 f,301 h, 301 j, 301 l, and 301 n are N magnetized. First, it is assumedthat the second coil 309 is energized such that the magnetic pole tooth306 a of the third yoke 306 is S magnetized, and the magnetic pole tooth307 a of the fourth yoke 307 is N magnetized.

Energization of the second coil 309 is interrupted in this state, and atthe same time the first coil 305 is energized such that the magneticpole tooth 302 a of the first yoke 302 is N magnetized, and the magneticpole tooth 303 a of the second yoke 303 is S magnetized. Then, anelectromagnetic force acting in a direction indicated by an arrow A isgenerated in the magnet 301 as shown in FIG. 15. It can be consideredthat the electromagnetic force acting in the direction indicated by thearrow A is comprised of a component acting in a direction of rotatingthe magnet 301 and a component acting along the axis of the magnet 301.

As stated above, the shake preventive guide bar 313 prevents the lensholder 310 fixed to the magnet 301 from rotating about the guide bar312, so that even when the component of the electromagnetic forcegenerated in the direction indicated by the arrow A, which acts in thedirection of rotating the magnet 301, is applied to the magnet 301, themagnet 301 is not rotated, but the lens holder 310, the lens 311, andthe magnet 301 are moved along the guide bar 312 by an electromagneticforce acting in a direction indicated by an arrow B in FIG. 15. Themagnet 301 is moved upward as viewed in FIG. 15, i.e. in the directionindicated by the arrow B, and is stopped at a position where themagnetized part 301 i is opposed to the magnetic pole tooth 302 a of thefirst yoke 302.

Then, energization of the first coil 305 is interrupted in this state,and at the same time the second coil 309 is energized such that themagnetic pole tooth 306 a of the third yoke 306 is N magnetized, and themagnetic pole tooth 307 a of the fourth yoke 307 is S magnetized. Then,electromagnetic force acting in the direction indicated by the arrow Ais generated again in the magnet 301. In this case as well, the magnet301 is not rotated by a component of the electromagnetic force generatedin the direction indicated by the arrow A, which acts in the directionof rotating the magnet 301, but the magnet 301, the lens holder 310, andthe lens 311 are moved along the guide bar 312 by a component of theelectromagnetic force, which acts in the direction indicated by thearrow B. The magnet 301 is moved upward as viewed in FIG. 15, i.e. inthe direction indicated by the arrow B, and is stopped at a positionwhere the magnetized part 301 a is opposed to the magnetic pole tooth306 a of the third yoke 306.

Then, energization of the second coil 309 is interrupted in this state,and at the same time the first coil 305 is energized such that themagnetic pole tooth 302 a of the first yoke 302 is S magnetized, and themagnetic pole tooth 303 a of the second yoke 303 is N magnetized. Then,an electromagnetic force acting in the direction indicated by the arrowA is generated again in the magnet 301. In this case as well, the magnet301 is not rotated by a component of the electromagnetic force generatedin the direction indicated by the arrow A, which acts in the directionof rotating the magnet 301, but the magnet 301, the lens holder 310, andthe lens 311 are moved along the guide bar 312 by a component of theelectromagnetic force, which acts in the direction indicated by thearrow B. The magnet 301 is moved upward as viewed in FIG. 15, i.e. inthe direction indicated by the arrow B, and is stopped at a positionwhere the magnetized part 301 h is opposed to the magnetic pole tooth302 a of the first yoke 302.

Further, energization of the first coil 305 is interrupted in thisstate, and at the same time the second coil 309 is energized such thatthe magnetic pole tooth 306 a of the third yoke 306 is S magnetized, andthe magnetic pole tooth 307 a of the fourth yoke 307 is N magnetized.Then, an electromagnetic force acting in the direction indicated by thearrow A is generated again in the magnet 301. In this case as well, themagnet 301 is not rotated by a component of the electromagnetic forcegenerated in the direction indicated by the arrow A, which acts in thedirection of rotating the magnet 301, but the magnet 301, the lensholder 310, and the lens 311 are moved along the guide bar 312 by acomponent of the electromagnetic force, which acts in the directionindicated by the arrow B. The magnet 301 is moved upward as viewed inFIG. 15, i.e. in the direction indicated by the arrow B, and is stoppedat a position where the magnetized part 301 n is opposed to the magneticpole tooth 306 a of the third yoke 306.

To drive the magnet 301, the lens holder 310, and the lens 311 in theopposite direction to the direction indicated by the arrow B, the firstcoil 305 and the second coil 309 are only required to be alternatelyenergized or deenergized in a sequence reverse to the above describedsequence.

As described above, in the present embodiment, the first coil 305 andthe second coil 309 are alternately energized or deenergized to switchthe polarity of each of the magnetic pole tooth 302 a of the first yoke302, the magnetic pole tooth 303 a of the second yoke 303, the magneticpole tooth 306 a of the third yoke 306, and the magnetic pole tooth 307a of the fourth yoke 307, whereby the magnet 301, the lens holder 310,and the lens 311 can be moved only in the direction indicated by thearrow B or in the opposite direction.

Further, in the present embodiment, it is possible to carry outmicro-step control such that the magnet 1 is stopped at a positioncorresponding to the magnitude of magnetic forces generated by the firstcoil 305 and the second coil 309, by controlling the magnitude ofelectric currents to be applied to the first coil 305 and the secondcoil 309. According to this micro-step control, the magnet 301 is stablyheld in a position where it is attracted by the two-phase coils, so thatthe lens 311 can be positioned more stably and accurately than by theconventional method using a voice coil actuator including a one-phasecoil.

As described hereinbefore, the conventional lens driving device of thetype which drives the lens along the optical axis by rotating a leadscrew by a stepping motor to move forward and backward a memberfunctioning as a female thread in mesh with the lead screw suffers fromthe problems that sliding noise is generated due to the engagement ofthe lead screw and the member as the female thread, and that it takestime to move the lens to a desired position due to a small pitch of thelead screw.

In contrast, in the present embodiment, the lens holder 310 and the lens311 are moved along the optical axis by alternately energizing ordeenergizing the first coil 305 and the second coil 309 to switch thepolarity of each of the magnetic pole teeth 302 a to 307 a of the firstto fourth yokes 302 to 307. As a result, it is possible to achieveexcellent quietness and high-speed driving of the lens 311.

Further, in the present embodiment, each of the magnetic pole tooth 302a of the first yoke 302, the magnetic pole tooth 303 a of the secondyoke 303, the magnetic pole tooth 306 a of the third yoke 306, and themagnetic pole tooth 307 a of the fourth yoke 307 has a flat plate shapeand extends along the corresponding one of the spiral magnetized parts301 a to 301 n on the outer peripheral surface of the magnet 301.

Now, let it be supposed that the magnet is not spirally magnetized, butas shown in FIG. 16, the magnet is magnetized such that S poles and Npoles are alternately arranged in a direction parallel with the opticalaxis. In FIG. 16, a first yoke is designated by reference numeral 402, asecond yoke by 403, a coil for magnetizing the yokes 402 and 403 by 405,a magnetized part of the first yoke 402 by 402 a, and a magnetized partof the second yoke 403 by 403 a. In this case, the magnetized parts 402a and 403 a are spaced apart from each other, which increase themagnetic resistance of the magnetic circuit, leading to a reduced outputof the lens driving device.

Alternatively, let it be supposed that a stator form is employed inwhich magnetized parts are formed as projections, as shown in FIG. 17,so as to make the magnetized parts closer to each other. In FIG. 17, afirst yoke is designated by reference numeral 502, a second yoke by 503,a coil for magnetizing the yokes by 505, a magnetized part of the firstyoke 502 by 502 a, and a magnetized part of the second yoke 503 by 503a. In this case, the dimension D (the width of the lens driving device)increases.

To solve the above problems, in the present embodiment, the magnetizedparts 301 a to 301 n are spirally arranged on the outer peripheralsurface of the magnet 301, and each of the magnetic pole tooth 302 a ofthe first yoke 302, the magnetic pole tooth 303 a of the second yoke303, the magnetic pole tooth 306 a of the third yoke 306, and themagnetic pole tooth 307 a of the fourth yoke 307 is formed into a flatplate shape and extends along the corresponding one of the spiralmagnetized parts 301 a to 301 n on the outer peripheral surface of themagnet 301. This makes it possible to realize a lens driving devicewhich is reduced in the dimension D (width thereof) and increased inoutput.

As described above, according to the present embodiment, the magnet 301is disposed between the first and second stator units, and the magneticpole teeth 302 a to 307 a of the first to fourth yokes 302 to 307 arespirally formed along the magnetized parts 301 a to 301 n in opposedrelation thereto. Further, the guide bar 312 is axially movably fittedin the guide part 310 b of the lens holder 310, with one end thereofrigidly fitted in the hole 314 d of the base plate 314. The shakepreventive guide bar 313 is slidably fitted in the groove 310 c of thelens holder 310, with one end thereof rigidly fitted in the hole 314 bof the base plate 314.

This makes it possible to provide a lens driving device which is capableof achieving reduction of zooming time during a zooming operation of thelens 311, enhancement of quietness in driving the lens 311, and stableand accurate lens positioning of the lens 311 (stability of a stopposition).

Although in each of the above described embodiments, the driving deviceis used for driving a lens, by way of example, this is not limitative,but the present invention is applicable to the driving of a member thatrequires stable and accurate positioning.

Further, although in each of the above described embodiments, the shakepreventive guide bar for preventing rotation of the lens holder isslidably fitted in the groove of the lens holder, by way of example,this is not limitative, but the mechanism for preventing rotation of thelens holder can have any suitable construction.

CROSS REFERENCE TO RELATED APPLICATION

This application claims priority from Japanese Patent Applications Nos.2004-307248 filed Oct. 21, 2004, and 2005-144197 filed May 17, 2005,which are hereby incorporated by reference herein.

1. A driving device for driving an object to be driven, the drivingdevice comprising: a hollow column-shaped magnet extending in adirection along a predetermined axis, the magnet having a plurality ofmagnetized parts spirally extending along an outer peripheral surfacethereof; a first stator unit having a first yoke, a second yoke, and afirst coil, each of the first yoke and the second yoke being formed of asoft magnetic material and having a plurality of magnetic pole teethextending in the spiral direction, each of the magnetic pole teeth ofthe first and second yokes being disposed in opposed relation to acorresponding one of the magnetized parts of the magnet, the first coilmagnetizing the first yoke and the second yoke, the first coil beinginterposed between the first yoke and the second yoke in the directionalong the predetermined axis; a second stator unit having a third yoke,a fourth yoke, and a second coil, each of the third yoke and the fourthyoke being formed of a soft magnetic material and having a plurality ofmagnetic pole teeth extending in the spiral direction, each of themagnetic pole teeth of the third and fourth yokes being disposed inopposed relation to a corresponding one of the magnetized parts of themagnet, the second coil magnetizing the third yoke and the fourth yoke,the second coil being interposed between the third yoke and the fourthyoke in the direction along the predetermined axis; a base plate towhich the first stator unit and the second stator unit are fixed in thedirection along the predetermined axis; a holding member that holds theobject to be driven and supports the magnet such that the magnet ismovable in the direction along the predetermined axis with respect tothe base plate; and a guide bar slidably fitted to a hollow part of themagnet, the guide bar guiding the magnet in the direction along thepredetermined axis, wherein the first coil and the second coil areenergized to move the holding member in the direction along thepredetermined axis to thereby drive the object to be driven.
 2. Adriving device as claimed in claim 1, wherein the magnet iscylindrically shaped.
 3. A driving device as claimed in claim 1, whereinthe magnet is prism shaped.
 4. A driving device for driving an object tobe driven, the driving device comprising: a hollow prism-shaped magnetextending in a direction along a predetermined axis, the magnet having aplurality of magnetized parts spirally extending along an outerperipheral surface thereof; a first stator unit having a first yoke, asecond yoke, and a first coil, each of the first yoke and the secondyoke being formed of a soft magnetic material and having a plurality ofmagnetic pole teeth extending in the spiral direction, each of themagnetic pole teeth of the first and second yokes being disposed inopposed relation to a corresponding one of the magnetized parts of themagnet, the first coil magnetizing the first yoke and the second yoke,the first coil being interposed between the first yoke and the secondyoke in the direction along the predetermined axis; a second stator unithaving a third yoke, a fourth yoke, and a second coil, each of the thirdyoke and the fourth yoke being formed of a soft magnetic material andhaving a plurality of magnetic pole teeth extending in the spiraldirection, each of the magnetic pole teeth of the third and fourth yokesbeing disposed in opposed relation to a corresponding one of themagnetized parts of the magnet, the second coil magnetizing the thirdyoke and the fourth yoke, the second coil being interposed between thethird yoke and the fourth yoke in the direction along the predeterminedaxis; a base plate to which the first stator unit and the second statorunit are fixed in the direction along the predetermined axis; and aholding member that holds the object to be driven and supports themagnet such that the magnet is movable in the direction along thepredetermined axis with respect to the base plate; and a guide barslidably fitted to a hollow part of the magnet, the guide bar guidingthe magnet in the direction along the predetermined axis, wherein thefirst and second coils are energized to move the holding member in thedirection along the predetermined axis to thereby drive the object to bedriven.